1. Field of the Invention
The field of the invention is semiconductor processing. More specifically, the invention relates to determining the location of a defect source which results in a localized elevation on the surface topography of a semiconductor substrate.
2. Background of the Invention
As the physical dimensions of semiconductor devices continue to decrease, the topography of the semiconductor substrate upon which the integrated circuit devices are formed becomes an important factor. A semiconductor processing step such as, for example, photolithography is used to pattern images in a photoresist on the surface of the substrate. The quality of the images formed on the surface of the substrate by photolithography is related to the topography of the substrate since the topography of the substrate can affect the focus of the photolithographic tool. Localized areas of relatively high elevation can result in defocusing of the patterned images in those areas, commonly referred to as “hotspots”. Hotspots are typically caused by a defect source such as, for example, foreign particulate matter trapped between the substrate and the photolithography aligner chuck upon which the substrate is placed. The foreign particulate matter causes the substrate to bend or deflect resulting in an elevation of a portion of the surface of the substrate above the foreign material. When the elevation deviation is large enough, the imaging surface will be out of focus relative to surrounding images, and imaging failure occurs resulting, typically, in a semiconductor device that will not function.
In order to detect hotspots so that corrective actions can be taken to prevent or minimize product yield loss, printed substrates are either visually scanned by a person with the naked eye, or are inspected by automated equipment. Visual scanning by the naked eye often only detects hotspots on those photolithographic patterns which are clearly repetitive such as high density patterns (e.g. nested lines/spaces). It is very difficult to detect hotspots on lithographic patterns with non-repetitive or isolated patterns (e.g. contact levels). In addition, visual scanning increases the risk of handling damage and defects on the substrate due to human contact. Automated scanning may detect imaging failure, but is not able to detect the root cause of the failure. For example, automated scanning may reveal that image quality is poor in a circular region on a given substrate but it does not indicate that this poor image quality is a result of a local defocus failure. Further, automated scanning requires expensive defect detection and analysis equipment.
Even when a hotspot is detected, visual or automated scanning techniques cannot determine whether the foreign particulate matter which caused the hotspot resides on the photolithography aligner chuck or on the substrate itself. Therefore, unnecessary maintenance activity may be performed on the chuck when the particulate matter is actually on the incoming substrates.
Determining whether the defect source which causes a hotspot is related to the substrate or the photolithography aligner chuck is desired.